1. Field of the Invention
This invention relates to a method for detecting rotten albumen and an apparatus therefor and more particularly to an optical method for recognizing rotten albumen in raw eggs and an apparatus therefor employing an optical filter.
2. Description of the Prior Art
Generally, production of processed egg products, e.g., mayonnaise requires a step of removing rotten albumen.
A recently developed system casts a beam of ultraviolet light with a wavelength in the range of about 300 to 410 nm and a peak intensity at about 365 nm onto the albumen of a broken raw egg and recognizes rotten albumen by checking for the presence of strong fluorescence from the rotten albumen.
As shown in FIG. 1, this system comprises an ultraviolet transmitter, not shown, a converging lens 1, an optical filter 2, a photoelectronic receiver 3, an amplifier 4 for an electrical output of the photoelectronic receiver 3, and a discriminating means, not shown, for recognizing whether or not the albumen is rotten.
Under the incident ultraviolet light, sound albumen produces only an extremely weak light-blue fluorescence while rotten albumen produces a strong, blue or green fluorescence due to the presence of the fluorescent material-producing fungi pseudomonas in the rotten albumen. The converging lens 1 receives the complex of the fluorescence and reflected ultraviolet light from the albumen under inspection and sends it to the optical filter 2. The optical filter 2 filters out ultraviolet light at wavelengths less than 400 nm and transmits the resulting fluorescence component to the photoelectronic receiver 3. In practice, a combination of tinted glass filters, e.g., L-42, Y-43, Y-44 and G-55 (JIS), all of which are trademarks of Toshiba Glass Co., Ltd., serve as the optical filter 2. The photoelectronic receiver 3 cuts off the fluorescence components at wavelengths exceeding 700 nm due to its optical properties thus passing only visible fluorescence components. GaAsP photodiodes are used as the photoelectronic receiver 3. The output of the photoelectronic receiver 3 is sent through the amplifier 4 to the discriminating means which compares the received signal level to an electrical reference level in correspondence to a predetermined threshold level of fluorescence from sound albumen and outputs a signal indicating the presence or absence of rotten albumen.
FIG. 2 shows the spectral transmissivity of the above-described optical filter 2 at a curve I, the relative sensitivity of the above-described photoelectronic receiver 3 at a curve II, the relative intensity of the fluorescence of rotten albumen at a curve III and the relative intensity of the fluorescence of sound yolk at a curve IV. The wavelength range of the curve III is almost fully contained within the range delimited by the curves I and II. The peak of the curve III falls at about 463 nm wavelength, almost coincident with the rising edge of curve I. Thus, the optical filter 3 isolates the low-wavelength end of the fluorescence spectrum with high efficiency and specificity.
However, the curves III and IV overlap in the range of abut 500 to 600 nm, especially about 520 to 570 nm. It is impossible to resolve rotten albumen if the threshold level segregating sound and rotten albumen should be set to a level, e.g. 50%, within the range of intensity due to fluorescence from the yolk. Thus this prior art system is not applicable to nonseparating-type automatic egg breakers which do not separate albumen from yolk. In addition, this prior art system could mistake sound albumen for rotten albumen in case of inadvertent admixture of sound yolk by a malfunctioning separating-type automatic egg breaker.